The Section is conducting patient-oriented research about the etiology, epidemiology, pathophysiology, genetics, diagnosis, and treatment of pheochromocytoma (PHEO) and paraganglioma (PGL). Projects include not only translational research-applying basic science knowledge to clinical diagnosis, pathophysiology, and treatment-but also reverse translation research where appreciation of clinical findings leads to new concepts that basic researchers can pursue in the laboratory. In order to achieve our goals, the strategy of the Section is based on the multidisciplinary collaborations among NIH investigators and outside medical centers/institutions. Our Section links together a patient-oriented component with two bench-level components. The patient-oriented component (Medical Neuroendocrinology) is currently the main driving force for our hypotheses and discoveries. The two bench-level components (Tumor Pathogenesis, Genetics, Chemistry & Biomarkers and Experimental Immunotherapies) emphasize first, technologies of basic research tailored for pathway and target discovery and second, the development of the discoveries into clinical applications. Clinical and genetic aspects of PPGLs Our knowledge of the susceptibility genes for PPGLs has increased; however, data on its impact on surgical decision-making has not been described. The aim of this study was to determine the effect of routine preoperative genetic testing on the operative intervention in patients with PPGLs. One-hundred-eight patients diagnosed with PPGLs who underwent 118 operations had preoperative genetic testing for 9 known PPGL susceptibility genes. A retrospective analysis of a prospective database was performed to evaluate clinical factors associated with the surgical approach selected and the outcome of the surgical intervention. In 51 patients (47%), a germline mutation was detected and one-third had no family history of PPGL. In 77 operations (65%), it was the first operative intervention for the disease site (60 laparoscopic, 17 open), and 41 (35%) were reoperative interventions (36 open, 5 laparoscopic). For initial operations, variables associated with whether an open or laparoscopic approach was used were tumor size (P=.009) and presence of germline mutation (P=.042). Sixty-eight adrenal operations were performed (54 total, 14 cortical-sparing). Variables significantly associated with a cortical-sparing adrenalectomy being performed were the presence of germline mutation (P=.006) and tumor size (P=.013). We concluded, that preoperative knowledge of the germline mutation status affects the surgical approach and extent of adrenalectomy. We also provided the first direct molecular genetic evidence of association between a somatic iron regulatory protein 1 (IRP1) loss-of-function mutation and pheochromocytoma and secondary polycythemia. In patients diagnosed with PPGL and polycythemia with negative genetic testing for mutations in HIF2A, PHD1/2, and VHL, IRP1 should be considered as a candidate gene. Imaging aspects of PPGLs We evaluated and compared diagnostic performance of 68Ga-DOTA(0)-Tyr(3)-octreotate (68Ga-DOTATATE) with 18F-fluoro-2-deoxy-D-glucose (18F-FDG) positron emission tomography-computed tomography (PET/CT) and anatomic imaging using computed tomography and/or magnetic resonance (CT/MR) imaging in detection of SDHx-related PPGLs in pediatric patients. Nine pediatric patients (5:4, girls:boys; 14.62.0 years) with an SDHx-related mutation (SDHB:SDHA:SDHD, n=7:1:1) were included. Here we demonstrated the superiority of 68Ga-DOTATATE PET/CT in localization of SDHx-related PPGLs in pediatric population compared to 18F-FDG PET/CT and CT/MR imaging with the exception of abdominal (excluding adrenal and liver) lesions, and suggests that it might be considered as a first-line imaging modality in pediatric patients with SDHx-related PPGLs. We have also found that MAX-related pheochromocytomas exhibit a marked 18F-FDOPA uptake, a finding that illustrates the common well-differentiated chromaffin pattern of pheochromocytomas associated with activation of kinase signaling pathways. We concluded that 18F-FDOPA PET/CT should be considered as the first-line functional imaging modality for diagnostic or follow-up evaluations for these patients. Metabolic aspects of PPGLs Metabolic aberrations have been described in neoplasms with pathogenic variants in the Krebs cycle genes encoding SDH, fumarate hydratase (FH) and isocitrate dehydrogenase (IDH). In turn, accumulation of oncometabolites succinate, fumarate, and 2-hydroxyglutarate can be employed to identify tumors with those pathogenic variants. Additionally, such metabolic readouts may aid in genetic variant interpretation and improve diagnostics. Using liquid chromatography-mass spectrometry, 395 PPGLs from 391 patients were screened for metabolites to indicate Krebs cycle aberrations. Multigene panel sequencing was applied to detect driver pathogenic variants in cases with indicative metabolite profiles but undetermined genetic drivers. Aberrant Krebs cycle metabolomes identified rare cases of PPGLs with germline pathogenic variants in FH and somatic pathogenic variants in IDH and SDH, including the first case of a somatic IDH2 pathogenic variants in PPGL. Metabolomics also reliably identified PPGLs with SDH loss-of-function (LOF) pathogenic variants. Therefore, we utilized tumor metabolite profiles to further classify variants of unknown significance in SDH, thereby enabling missense variants associated with SDH LOF to be distinguished from benign variants. We proposed incorporation of metabolome data into the diagnostics algorithm in PPGLs to guide genetic testing and variant interpretation and to help identify rare cases with pathogenic variants in FH and IDH. Therapeutic aspects of PPGLs: Cluster I PPGLs tend to develop malignant transformation, tumor recurrence, and multiplicity. Transcriptomic profiling suggests that cluster I PPGLs and other related tumors exhibit distinctive changes in the TCA cycle, the hypoxia signaling pathway, mitochondrial electron transport chain, and methylation status, suggesting that therapeutic regimen might be optimized by targeting these signature molecular pathways. In the present study, we investigated the molecular signatures in clinical specimens from cluster I PPGLs in comparison with cluster II PPGLs that are related to kinase signaling and often present as benign tumors. We found that cluster I PPGLs develop a dependency to mitochondrial complex I, evidenced by the upregulation of complex I components and enhanced NADH dehydrogenation. Alteration in mitochondrial function resulted in strengthened NAD+ metabolism, here considered as a key mechanism of chemoresistance, particularly, of succinate dehydrogenase subunit B (SDHB)-mutated cluster I PPGLs via the PARP1/BER DNA repair pathway. Combining a PARP inhibitor with temozolomide, a conventional chemotherapeutic agent, not only improved cytotoxicity but also reduced metastatic lesions, with prolonged overall survival of mice with SDHB knockdown PPGLs allograft. Our findings provided novel insights into an effective strategy for targeting.